This is to supplement several existing threads in the CTS and CTS-V forums related to drive shaft coupler discs (aka
guibos) with a complete story that covers the Revshift replacement coupler and transmission mount shimming issues.

My car: 2006 CTS 3.6 w/ 6 speed manual, 89k miles

Symptoms/Diagnosis: I began experiencing vibration while driving at highway speeds (thats 65 - 80 mph, here in N.M.). I noticed that the vibration went away under acceleration and with engine braking. The vibration became worse over the course of a couple of months/3,000 miles, to the point where I felt like something was definitely wrong, but not to the point where the car wasn't drivable. Because of the pattern the vibration stopping when the driveshaft was loaded, I suspected a driveshaft coupling failure, or possibly a bad rear wheel bearing. I put the rear on jack stands and ruled out the wheel bearing hypothesis, then crawled underneath to check the driveline. The rear coupling at the differential looked okay, but I could see movement at the coupler between the transmission and the drive shaft, to the point where I could see daylight around the bolts when I rotated the shaft (also could feel play w/ rotation). (Note on how long you can drive with a bad coupler: after I made the diagnosis and was waiting for the part to arrive, the situation deteriorated to the point where I didn't feel comfortable putting a lot more miles on the old disc.)

Below is a pic of the busted rubber coupler I took out of the car. Basically, by the time it came out, all the steel inserts were loose from the rubber with a 1/4" of play, and the steel was cracked and broken in places.

The Replacement Part: As has been covered in the other threads, GM does not sell the the rubber drive shaft coupler discs by themselves, but they will sell you a complete driveshaft assembly. Too expensive and wasteful. Options I considered:

Used from a junkyard - not a good practice for wear parts, IMO, but if you're not picky, there are a bunch of driveshafts listed on eBay.

Deutsche AutoParts advertises OEM discs on eBay, for ~ $170/pair. At least one user here has posted that he had problems with them and their discs. I also read through a bunch of other posts about the possibility of using a OEM disc for BMW or Mercedes - these threads conclude that these discs don't work in the CTS.

Revshift makes a replacement disk out of billet aluminum, with polyurethane inserts. I decided to go w/ the RevShift disc, which they sell from their website for $139 + $10 shipping. The Revshift disc is the correct size and fit, and includes extended sleeves that act as locators. It did take 2 weeks for me to get the part after my order.

Installing the Coupler: Jack the car up on all four corners and use jack stands. Put it in neutral w/ the parking brake off b/c you'll need to rotate the driveshaft. Drop the exhaust (mandatory, you won't be able to access the coupler bolts with the exhaust in place). Use paint to mark the end of the driveshaft and the transmission flange, so that you can reconnect things with the same orientation. Use a breaker bar to loosen the 6 bolts. Remove the six bolts. Be ready to support the front of the driveshaft with something so that it doesn't sag more than 4"-6" (it feels like it might slide out of the central joint if it's not supported). Remove the rubber coupler and insert the Revshift part and use all six bolts to locate things together. Install the nuts on the drive shaft side bolts. Use the extra washers Revshift includes. At this point, I notices that the surface of the disc and the flange coming out of the tranny were not parallel, so that things pieces touched at the top, but had a 1/8" gap at the bottom (more on this below). I rotated the driveshaft and bolted it together at the top, to ensure that the extended sleeve was properly positioned before tightening each bolt. Torque the bolts to 63 ft-lbs. Reinstall the exhaust, drop the car, and go for a test drive. All this should take an hour to an hour or so, depending on how experienced you are at dropping the exhaust.

Shimming the transmission mount: If you're lucky, you won't need any of this - your car will feel great once you install the Revshift disc. Mine didn't! I experienced strong vibration, beginning at 20 mph. It was most pronounced in the gearshift lever and you could see the gearshift moving back and forth. I am going to skip most of the naarrative about how I screwed around with the thing over the course of a couple of weeks and just tell you what you need to know:

The Revshift disc is stiffer than the stock rubber part. Less tolerance for vertical misalignment = more vibration.

Your transmission mount may have compressed, but I think it's unlikely that the amount of misalignment I found in my car (0.20") could have arisen that way, I think it was never exactly aligned. The problem was masked by the softer stock rubber coupler. Whether its a worn mount or a misalignment, I suspect this is why my coupler failed.

The geometry of the driveline is different when the car is jacked up then it is on the ground. The only way to figure out how much to shim your transmission is trial and error, with driving the car on the road to test.

Raise the front on jackstands far enough off the floor for you to work comfortably underneath. Loosen the two nuts holding the transmission mount to the frame cross bar. Put a block of wood on your floor jack and put it under the tranny, jack gently until you lift the tranny 1/4" off the cross bar. Now you can loosen the bolts holding the crossbar to the chassis. You will need a Torx T-50 bit.

Use 3/16" fender washers with a slot cut out as temporary shims between the crossbar and the transmission mount (trick I read about on the forum). You will not be able remove the crossbar in order to get an intact washer placced w/o dropping the exhaust. You don't want to do this while you are in the trial and error stage.

My car got pretty smooth with 3 washers, but wasn't consistently smooth. It got worse w/ 4. I made permanent shims from some flat aluminum scrap I had in the garage, drilling appropriate holes. See the pictures. It seems pretty good w/ the permanent shims, but if I start experiencing occasional roughness, this will mean that the geometry is not stable enough for the aluminum Revshift coupler and I'll have to put in a rubber coupler (or a complete aftermarket driveshaft replacement with a universal joint at the front).

i wonder if you would still have the vibrations if you used the ones that are full poly with metal inserts by creative steel.
ive got 1 of them...it was suppose to go in but......well....no surprise... im lazy.

i wonder if you would still have the vibrations if you used the ones that are full poly with metal inserts by creative steel.
ive got 1 of them...it was suppose to go in but......well....no surprise... im lazy.

When I checked the CS website, it looked like they only made it for CTS-V, not the six cylinder.

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Originally Posted by carrnuttdave

DDo you think replacing the mount when replacing the guibo would take care all the trial and error in coming up with the proper shim?

Don't know. I would have tried replacing the mount if my dealer had it in stock, but since it was a 5 day wait and I wanted to drive the car, I experimented with shimming using washers. For future reference, the trans mount for a 3.6 manual tranny is 15861894. List price is $185, but there's dealer on the internet who sells it for $124 (they didn't have it in stock, either).

What condition was your center carrier in? Ive got the same issue with mine as I today replaced my front unit also. I did notice the center carrier is not centered and wondering if that might be an issue too.
Ive got like 86xxx and some change for milage on mine. What kind of milage you have on yours? Also how many clutches have you had to do on your car?

The geometry of the driveline is different when the car is jacked up then it is on the ground. The only way to figure out how much to shim your transmission is trial and error, with driving the car on the road to test.

You could put the jack stands under the control arms on each end of the car. That way the driveline geometry would be normal and you could eliminate the trial and error.

What condition was your center carrier in? Ive got the same issue with mine as I today replaced my front unit also. I did notice the center carrier is not centered and wondering if that might be an issue too.
Ive got like 86xxx and some change for milage on mine. What kind of milage you have on yours? Also how many clutches have you had to do on your car?

Cgouldin: I'm at 89k miles, original clutch. When 80% of your miles are on the interstate, clutches last a pretty long time (the orig clutch on my '96 cavalier convertible w/ the 2.4l last 170k). My center carrier seems ok, by I haven't inspected it closely.

I got the Revshift one also for the front. I'm thinking because I was unaware of how critical it is; that I clocked the propshaft in wrong. Ive got a friend at the GM Tech center who advised me on the marks and will be trying to see about it this weekend if the weather holds out.

Buyers beware !
Revshift states that they have the only alternative to buying the whole driveshaft from the dealer...They also say, on their website that the flexdisc has a lifetime warranty. After contacting Revshift many times to insure I was getting the right part for my 2007 Cadillac CTS, they reassured me that the piece would "fit like a new one". They also said that they sell many of those a week. They invoiced on my credit card really quickly, took two weeks to get the part. When I got the part, I had it installed by a professionnal qualified Cadillac technician, the part itself fit. The moment the car went over 40km an hour it vibrate a LOT. After contacting Revshift to tell them I was not satisfied and would be returning the part. They sent a reply email, now the "perfect fit" part sometimes did not fit perfectly and this was surely du to misalignement with my transmission or driveline, and so very kindly attached a complete installation procedure to chim my transmission. Sorry the REvshift, I am not shimming my transmission for your 139$ piece of shit....and would not refund because the part was installed (how else can you find out if it fits). The "engineers" at Revshift does not properly balance their piece of shit part. Seller going under "WHO517" on Ebay, check feedback for same part. DO NOT BUY FROM HIM ! This part does NOT replace the OEM part from GM. Low class company, low class engineer, low class warranty, and high class RIP OFF, Fraud !

Buying the piece new from the dealer, they honor their warranty, customers, and no shims needed to align the transmission WTF ?

Maybe you've unlocked this OD, my first thought was of another poster who had a similar experience and I suggested to him to retrace his steps and sure enough he had not inserted the guibo fully. He pressed it in firmly and the 40 mph vibration disappeared entirely.

This guy was so irate I didn't bother to answer him. If it takes shimming, it takes shimming, what's the big deal ?

Apologies if you neglected to lock it. No intent to act contrarily to your intent.

Originally Posted by odthetruth

I have edited the above post and closed this thread for now until I can clear everything up.